Seagrasses are vascular plants (not true grasses) comprising ~50 temperate and tropical species within 2 families.


Given that seagrasses are vascular plants, should they be capable of colonizing sediments in area of moderate wave and current energy?  High current energy?


Seagrasses can propagate using rhizomes, but also sexually involve underwater pollination and seed production.   Both the leaves and rhizomes can absorb nutrients directly.  How is this a potential advantage over seaweeds in low nutrient environments?  The aquatic medium has eliminated the need for a fibrous support system as found in terrestrial plants and flexibility allow seagrasses to withstand wave action.

Most seagrass are rooted below the level of low tide. 
What effect does water clarity have on seagrasses, and seagrasses on water clarity?


 

Seagrass often form extensive single-species meadows covering large areas of the bottom within a given depth range, frequently resulting in strong zonation suggesting that competition among seagrass species may be important.  Horizontal distribution may possibly be mediated by differential abilities to acquire nutrients.  Macroalgae (such as Caulerpa taxifolia) are associated with seagrass die-back, possibly as a result of interference competition via the production of toxic secondary metabolites.

http://www.flmnh.ufl.edu/fish/southflorida/seagrass/Zonation.html

The stabilizing effects of seagrasses on bottom sediment promotes the establishment of macroalgae and infaunal invertebrates.  How would the physical structure of seagrasses affect the exchange of planktonic larvae and detritus from the water column?

Seagrass systems are highly productive (both primary and secondary), yet herbivory on seagrass is limited and relatively few species include seagrasses as a major part of their diet (sea turtles, manatee, geese, some urchins, some fish, some amphipods...).  The reason is that seagrasses are fiberous and contain compounds that are difficult to metabolize (especially phenolic compounds that may act as an anti-fouling defense).

How can secondary production (i.e. consumer production) be high if few species are consuming seagrass tissue?


Seagrass epiphytes may contribute more than one-third to the total above ground biomass and 30% to combined seagrass/epiphyte productivity.   Epiphytes appear to  provide a more assimilable food source  for  animals such as snails that were previously assumed to be 'detritivores'. 

So, what would a food web/energy diagram look like for a seagrass ecosystem?

Predation on seagrass herbivores has also been invoked to explain limited consumption of seagrass.   "Halos" around patch reefs suggest that herbivory is only intense near where the reef provides refuge for large herbivores.

Epiphytes are not only important in channeling energy to higher trophic levels, but also have negative effects on seagrasses (how?).  Experimental exclusion of epiphyte grazers can reduce seagrass growth rates.